The present invention relates to an autodepositable adhesive, particularly an adhesive for bonding an elastomeric material to a metallic material.
It is generally known that the corrosion resistance of metal substrates can be improved by coating the substrate with an autodeposition composition that generally comprise an aqueous solution of an acid, an oxidizing agent and a dispersed resin. Immersion of a metallic surface in an autodeposition composition produces what is said to be a self-limiting protective coating on a metal substrate. The general principles and advantages of autodeposition are explained in a multitude of patents assigned to Parker Amchem and/or Henkel (see, for example, U.S. Pat. Nos. 4,414,350; 4,994,521; 5,427,863; 5,061,523 and 5,500,460). However, to the best of the inventors' knowledge these autodeposition compositions have not been successfully used as one coat adhesives or covercoat adhesives.
Elastomer-to-metal bonding is subjected to severe environmental conditions in many industrial and automotive assemblies. For example, many engine mounting assemblies that employ elastomer-to-metal bonding contain fluids in order to assist in damping of vibration of the engine. These fluid-filled engine mounting devices are being increasingly exposed to high temperatures such that the elastomer-to-metal adhesive bonds within the mounts are being exposed to very high temperature fluid environments. Many elastomer-to-metal assemblies, particularly those utilized in automobile applications, are routinely exposed to materials that contain corrosive salts or other corrosive materials that may act to degrade the elastomer-to-metal adhesive bond.
In light of the increasing regulations regarding volatile organic compounds (VOC), the use of traditional solvent-borne adhesives is becoming more problematic. Consequently, there is significant ongoing work to develop water-borne replacements. Current aqueous adhesives suffer from user drawbacks. Application of an adhesive by dipping the adherend in a bath of the adhesive is frequently preferred by the user due to its simplicity. However, dipping of aqueous adhesives leads to problems with controlling the film thickness and dripping.